Trends of Structure Degradation of VVER-1000 Reactor Pressure Vessel Steels Determining Their Performance at Lifetimes of over 60 Years

Changes in the structural state of steels of VVER-1000 reactor pressure vessels (RPVs) at an extended lifetime of 60 years and more were considered. A comprehensive analysis of available experimental data on changes in the structural state of RPV materials under irradiation was carried out. Extended dose dependences of the accumulation rate of radiation-induced structural elements and grain-boundary segregation of phosphorus are presented. The nature of changes in strength characteristics and critical brittleness temperature of RPV materials due to irradiation was shown. A preliminary estimate of the lifetime of RPV steels depending on their nickel content was made basing on the study of trends in the volume density and average size of radiation-induced structural elements, radiation defects, and radiation embrittlement mechanisms.